1. Field of the Invention
The present invention relates to a data recording/reproducing system for an optical recording medium, and more particularly, to a device and method for generating an optimal writing signal for an optical recording medium.
2. Background of the Related Art
In general, an optical medium, such as a re-writable optical disk, is formed of a phase change material. A beam focused from an optical head is converted into heat, and the heat changes a state of the phase change material, which changes a reflection of the phase change material, that forms a mark on the phase change disk, to record a pit. The formation of a fixed length of mark on the disk is called as write strategy. In this instance, the laser beam is incident on an opposite side of a reflection surface where the pits are formed. The pits are projections if they are seen from the laser incident side. The pit has a width of 0.4xcx9c0.6 xcexcm, and a length of the pit and a distance between the pits has 9 steps from 3T to 11T in the case of a compact disk(CD), and 12 steps from 3T to 14T in the case of digital versatile disk(DVD). The xe2x80x98Txe2x80x99 is a length of one clock pulse, with 3T meant three clock pulses, and 11T meant a length corresponding to 11 clock pulses. In groups of pits in a spiral track, there are particular array of pits at fixed intervals, one of which is a synchronizing signal, and a block between adjacent synchronizing signals is called a frame which consists of a plurality of symbol data.
FIG. 1 illustrates a block diagram showing a system related to recording in a related art optical disk recording/reproducing device, including an encoder 103 which processes the steps for receiving a signal for recording on a disk 101, converting the signal into 16 bit digital signal, and splitting the signal into forward 8 bits and a backward 8 bits (this is called as a symbol) in frame units, and conducts an EFM (Eight to Fourteen Modulation) in which a data of symbol 8 bits are converted into 14 bit data by taking a 14 bit code value from a code table in a memory (not shown). That is, the memory has the code table for conducting an EFM or EFM+ mapped thereon. The data having EFM or EFM+ modulated is added with margin bits (for example, three bits), and subjected to modulation of NRZI (Non-Return-to Zero, Inverted) type as shown in FIG. 2A. The NRZI modulation is a modulation rule in which a data is inverted a signal of xe2x80x981xe2x80x99. That is, once xe2x80x981xe2x80x99 is met, the present state is inverted. In the meantime, a writing power generator 104 generates a power of an LD (Laser Diode) for a data to be written, converts it into an analog signal, and provides to an LD driver 106 through a writing level adder 105. The writing power is varied with a length of mark to be formed and a state of the disk.
Upon reception of the NRZI modulated data from the encoder 103, the LD driver 106 modulates the LD power into a writing power, i.e., converts an LD driving voltage into an LD driving current, and drives the LD of an optical pickup 102, to write the NRZI modulated signal on the optical disk 101. The LD beam power varies with temperature significantly; the writing power drops the more, as the temperature rises the higher, and vice versa. In order to solve this problem, a portion of the LD power is fed back to an ALPC (Auto Laser Power Control) feed-back 107. The ALPC feed-back 107 provides a xc2x1 power level to the writing level adder 105 according to a fed-back LD power, and adds to the writing power generated at the writing power generator 104, for maintaining the LD power at a fixed level during writing/reproduction.
When a data is written by means of an NRZI modulated single pulse, the pit is formed like a tear drop due to a thermal property of the disk itself, or formation of the mark is distorted due to a latent heat property of the disk. That is, a fore end of a mark being written at the present time is affected by a latent heat generated for forming a mark written just before, to change a length of the mark, and to change an end length of the mark written at the present time according to a length of the mark written at the present time. Accordingly, a multi-pulse modulation is used at times for preventing dispersion of the heat and forming a smooth oval form of a pit, in which, as shown in FIG. 2B, one pulse is divided into many pulses by turning on/off many times within one NRZI modulated pulse before directing to the disk. The direction of many divided pulses to the disk can prevent accumulation of heat in a section of a signal pit, to form the smooth oval form of pit. Alikely, upon reception of a multi-pulse modulated signal from the encoder 103, the LD driver 106 converts an LD driving voltage into an LD driving current before driving the LD, the multi-pulse modulated signal is written on the optical disk 101.
As shown in FIG. 2B, an order of strength of the LD power is at writing, which is the strongest, at erasure, and at reading. However, since widths and intervals of the multi-pulses are fixed, the problems caused by the heat dispersion or accumulation according to lengths of pits formed as marks, and lengths of blanks where no data is written thereon can not be solve completely. This implies that, despite the pit should have a form like one shown in FIG. 2E, actual one is not so. That is, lengths of prior marks and blanks vary widely, and a ratio of the heat dispersion varies with the lengths of marks and the blanks, which affects the formation of a pit of the next mark that is exhibited as a jitter in a reproduction signal. Particularly, an overwritten pit becomes either greater or smaller than a desired pit, which acts as a main cause of jitter in reproducing a data from the disk, and makes an accurate data recovery difficult. In order to solve this problem in a related art, the writing pulse is mainly adjusted with respect to a time axis in writing the data. One of which methods is the pulse edge shift as shown in FIG. 2C, and the other method is the pulse position shift as shown in FIG. 2D. That is, as shown in FIG. 2C, in the edge shift, a desired mark is formed by adjusting an edge of a writing pulse of the present mark with respect to a time axis according to lengths of a prior mark, prior blank and the present mark being formed, and, as shown in FIG. 2D, in the pulse position shift, a desired mark is formed by adjusting a width of a writing pulse with respect to the time axis according to the lengths of the prior mark and the prior blank, and the length of the present mark being formed.
However, the method for adjusting a width of a writing pulse with respect to the time axis is difficult to control as it goes to high speed/high density, with a high frequency noise exhibited. For example, a fine pulse width adjustment in a range of approx. 1 ns is required for a DVD-RAM(for example, of 4.7 GB), which is difficult to control as functions of the length of a pit to be written and a length of a blank forward of the pit to be written and the like, and, even if the adjustment is made, it is difficult to form a desired mark. And, this can not be followed after by a device for implementing this with easy. That is, as it goes to high speed/high density, a time basis control of the writing pulse becomes difficult.
Accordingly, the present invention is directed to a device and method for generating an optimal writing signal for an optical recording medium that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a device and method for generating an optimal writing signal for an optical recording medium, which is easy to control and permits to form an accurate pit.
Another object of the present invention is to provide a device and method for generating an optimal writing signal for an optical recording medium, which permits an optimal writing.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for generating a writing signal for an optical recording medium according to an embodiment of the present invention, includes the steps of (1) confirming a length of a prior blank and a length of the present pit from the writing pulse, (2) providing a writing power compensating signal such that a writing power level of a starting portion of the pit is determined with reference to the length of the prior blank confirmed in the step (1), and a writing power level of the end portion of the pit is determined with reference to the length of the present pit, and (3) adding the provided writing power compensating signal to the writing power level.
The step (2) includes the steps of inverting the writing pulse, and integrating the inverted signal.
The step (2) includes the step of bringing an initial power for a blank portion of the integrated signal to a reference level by using a reset pulse.
The step (2) includes the step of subjecting the integrated signal to a non-linear transformation.
The step (2) includes the steps of charging within a blank section of the writing pulse, and discharging within a pit section, for providing the writing power compensating signal.
The step (2) includes the steps of bringing an initial level of the blank portion to the reference level by charging from the reference level.
In other aspect of the present invention, there is provided a device for writing/reproducing to/from an optical recording medium according to an embodiment of the present invention, including an encoder for generating the writing pulse according to a data to be written, a writing power compensating signal generator for providing a writing power compensating signal such that a writing power level of a starting portion of the pit is determined with reference to the length of the prior blank confirmed from the writing pulse, and a writing power level of the end portion of the pit is determined with reference to the length of the present pit, and an adder for adding the provided writing power compensating signal to the writing power level.
The writing power compensating signal generator includes an integrator for generating the writing power compensating signal by inverting the writing pulse, integrating the inverted signal.
The integrator brings an initial power of the blank portion of the integrated signal to the reference level by the reset pulse.
The writing power compensating signal generator includes a charger/discharger for generating the writing power compensating signal by charging within a blank section of the writing pulse and discharging within a pit section of the writing pulse.
The writing power compensating signal generator subjects the writing power compensating signal to non-linear transformation, and forwards to the adder.
The encoder generates a single pulse as the writing pulse for a one pit length.
The encoder generates multi-pulse as the writing pulse for one pit length.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.